How to make a coffin in Sketchup (a walkthroug)

Brace yourselves. Helloween is coming.
This one is for people who don't take their life too seriously.
I really do not know why would you need a tutorial like this. Maybe you have 3d printer and wanna make decorations? Or maybe you wanna enter the funeral business, and learn how to design your merch by yourself?
In this case here's something 4 a start.